java 接口的定义即实现

package test;
interface CalInterface
{
final float PI=3.14159f;//定义用于表示圆周率的常量PI
float getArea(float r);//定义一个用于计算面积的方法getArea()
float getCircumference(float r);//定义一个用于计算周长的方法getCircumference()
}

/*class Circle implements MM
{
double r;
Circle(double r){this.r=r};
void getarea(double r){ System.out.println(pi*r*r);}
void getsize(double r){ System.out.println(pi*r*2);}

}*/
public class main implements CalInterface
{
public float getArea(float r)
{
float area=PI*r*r;//计算圆面积并赋值给变量area
return area;//返回计算后的圆面积
}
public float getCircumference(float r)
{
float circumference=2*PI*r;      //计算圆周长并赋值给变量circumference
return circumference;           //返回计算后的圆周长
}
public static void main(String[] args)
{
main c = new main
();
float f = c.getArea(2.0f);
System.out.println(Float.toString(f));
}
}